The present invention relates to improvements in apparatus for monitoring the external surfaces of moving objects, and more particularly to improvements in apparatus for optical scanning or monitoring of the exterior of moving rod-shaped commodities, such as cigarette rods, filter rods and other rod-shaped products of the tobacco processing industry. Still more particularly, the invention relates to improvements in optical scanning apparatus of the type wherein radiation is directed against the external surface of a moving rod and the radiation which is reflected by the external surface of the rod is evaluated in order to ascertain the condition of monitored portions of the external surface.
Defects in the wrappers of rod-shaped products of the tobacco processing industry cause more or less pronounced changes in the characteristics of light or other types of radiation which is reflected by the external surfaces of such products. For example, a hole in the wrapper of a cigarette rod or filter rod will cause a pronounced change in the intensity of reflected radiation and such changes can be detected by photoelectric transducers to generate signals which are indicative of fluctuations of the reflected radiation. The signals can be evaluated and used, for example, to segregate defective rod-shaped articles from satisfactory articles. Analogously, adhesive spots or printed matter on the wrappers of cigarette rods or the like reflect radiation differently than the remaining portions of the external surface of the wrapper of a cigarette rod, filter rod or the like. The presence of a hole in the wrapper of a cigarette rod entails a reduction of the intensity of reflected radiation because the effect of the hole is the same as that of a dark spot on the normally white cigarette paper. On the other hand, a spot of glue on the exterior of the wrapper of a cigarette rod entails a more pronounced reflection of impinging radiation so that the presence of such adhesive spot can be detected by converting reflected radiation into a signal of more pronounced intensity than anticipated for the scanning of a satisfactory portion of the wrapper. In this manner, an optical scanning system can ascertain the presence or absence of a variety of defects including holes in the wrappers, the absence or improper application of imprints, the presence or absence of adhesive spots, smudges and/or a combination of the above. Moreover, such optical scanning systems can also be used to ascertain whether or not an imprint is sufficiently dark or is applied in the proper color because the extent of reflection of radiation by an imprint which is applied to the exterior of a wrapper consisting of cigarette paper or the like fluctuates or varies in dependency on the tone or shade of the coloring agent which is used for the application of imprints. In other words, by properly evaluating the reflected radiation, a suitable electronic or other evaluating system can categorize the defects and can generate signals which are then used for segregation of defective smokers' products from satisfactory products if the intensity of signals denoting particular defects is sufficiently pronounced or sufficiently low to warrant such segregation.
U.S. Pat. No. 4,350,170 granted Sept. 21, 1982, to Baier discloses an apparatus for monitoring the exterior of a moving cigarette rod or the like. The patented apparatus employs a ring-shaped light-conducting prism which is mounted in an annular housing surrounding a portion of the path for a moving cigarette rod or the like. The prism is designed to direct light at an acute angle to the axis of the moving rod, and the light which is reflected by the exterior of the moving rod passes through an annulus of light-conducting fibers each of which directs reflected light against a discrete photoelectronic transducer. Signals which are generated by the transducers are evaluated and utilized for segregation of defective cigarettes from satisfactory products. In addition, such signals can be utilized to adjust the machine which turns out the rod so as to ensure that the defects which happen to recur at frequent intervals or continuously can be eliminated with little loss of time.
An advantage of the patented apparatus is that, due to impingement of light at an acute angle to the axis of the moving rod, such apparatus can increase the contrast between the signals which are indicative of satisfactory and unsatisfactory portions of the exterior of the moving rod. In other words, this apparatus can ascertain the presence of pronounced as well as smaller defects with a high degree of reliability. However, the patented apparatus also exhibits a drawback, namely that light beams which are directed against the exterior of the moving rod at an acute angle to the axis of the rod cause the development of pronounced shadows as a result of detection of folds or undulations in the wrapping material which are not necessarily indicative of unsatisfactory portions of the wrappers but are interpreted as such by the evaluating system of the patented apparatus so that the corresponding rod-shaped articles are segregated even though their wrappers are satisfactory for further processing (such as packing) of the corresponding articles.